There’s no doubt about it now: The gloves have come off between Cory Booker and Frank Lautenberg.

The Newark mayor has announced — no ifs, ands or buts — that he’s gunning for Lautenberg’s US Senate seat next year.

Problem is, Lautenberg and Booker are both Democrats. And the senator, who turns 89 next week, has given no definitive sign that he’s ready to call it quits.

In fact, he reportedly considers Booker’s decision to jump the gun before waiting for his own decision “shameful.”

For now, Booker can afford to be smug. No doubt he’s seen the recent Fairleigh Dickinson poll that shows him leading Lautenberg by better than 2-to-1.

It might be easy to feel sympathy for Lautenberg as he finds himself being elbowed out of politics — New Jersey-style, to be sure — by his younger challenger.

Until you remember just how Lautenberg returned to the Senate a decade ago.

Back in 2002, Lautenberg had already retired from the seat he’d held for three terms.

Then, about a month before the election, Democratic Party officials stepped in to substitute Lautenberg for scandal-scarred Sen. Robert Torricelli — who’d won the primary but withdrawn from the general election when polls showed him tanking.

This, despite a state law that plainly prohibited such last-minute substitutions.

Lautenberg joined the race, and the state’s Supreme Court, in an out-and-out bit of political shuffleboard, approved the switcheroo, saying “the public interest” trumped the clear meaning of the law.